People drink diet soda to avoid calories and keep from getting fat. Yet study after study shows that daily use of artificial sweeteners is strongly associated with obesity. Do overweight people tend to drink diet soda, or does diet soda cause people to become overweight?

A number of recent studies make it clear: artificial sweeteners cause obesity. They confuse the body, causing appetite to increase and metabolism to slow. When something tastes like it should have calories but does not, you eat more and get fatter from what you eat. The same effect has been found with fat substitutes.

You can’t get something for nothing. Everything you consume has a cost. It’s ironic that the cost, in this case, is obesity.

Two Longitudinal Studies of Diet Soda

Two large longitudinal studies were recently completed. They showed that people who drank diet soda every day were much more likely to become overweight or obese, and to develop metabolic syndrome and type 2 diabetes. Metabolic syndrome increases the risk of cardiovascular disease and type 2 diabetes, and is associated with obesity.

In August 2008, Sharon P. Fowler and associates published a 9-year longitudinal study, covering 1979-1988, on the relationship between artificially sweetened beverages and obesity. They found that drinking more than 21 diet sodas per week was associated with almost double the risk of being overweight or obese, regardless of the baseline BMI. So even if people didn’t start off fat, if they drank more than 21 diet sodas per week, they were twice as likely to become fat by the end of the study.

In January 2009, Jennifer Nettleton and associates published a 7-year longitudinal study, covering 2000-2007, tracking diet soda consumption, type 2 diabetes, and metabolic syndrome in over 6800 people aged 45-84. Metabolic syndrome was defined using National Cholesterol Education Program Adult Treatment Panel III criteria, which requires at least three of the following:

Those consuming 1 or more diet sodas per day had a 36% higher risk of metabolic syndrome than non-consumers, and a 67% higher risk of type 2 diabetes. This wasn’t due to a particular artificial sweetener since the artificial sweetener used changed over the 7-year period.

These longitudinal studies strongly suggest that artificial sweeteners cause obesity, but only controlled lab studies can offer proof. Finally we have this.

Artificial Sweeteners Confuse the Body

Susan Swithers and Terry Davidson, psychologists at Purdue University, have done a series of controlled studies that show that animals (like rats and humans) appear to use sweet taste to predict the caloric contents of food. Eating sweet noncaloric substances degrades this predictive relationship, leading to increased food intake and lowered metabolism.

In a 2008 study [PDF], some rats were given yogurt sweetened with saccharin, and some were given yogurt sweetened with glucose. Those given the artificially sweetened yogurt ate more food, gained more weight, and gained more body fat. Two changes accounted for this:

Their caloric compensation ability was reduced. That is, they were less able to adjust for excess calories by reducing intake at a later time.

They showed a "blunted thermic response" to sweet-tasting diets. When you are about to eat, the look and the smell of the food causes your metabolism to speed up, and this is measurable as an increase in body temperature – the "thermic response". When the rats used to artificial sweeteners ate sweet foods, their metabolisms didn’t rev up as much. The artificial sweeteners had taught the rats that sweet foods have no calories, so eating naturally sweetened food caused greater than normal weight gain.

These results were reproduced and extended in a 2009 study. In addition to saccharine and low-fat yogurt, the rats were given acesulfame potassium as the artificial sweetener and refried beans as the food. The researchers chose refried beans because they have about the same calories as low-fat yogurt, but a different nutritional profile. The previous results held, plus the researchers found that the effects were resistant to reversal. The rats given the artificial sweeteners continued to gain weight after the artificial sweetener was withdrawn.

Note that weight gain would be expected with any no-calorie sweetener used daily, even a natural one like stevia. Stevia doesn’t have the chemical risks of an artificial sweetener, but it confuses the body in the same way. Coca Cola markets a stevia-based sweetener called Truvia, and PepsiCo markets one called PureVia. They are both starting to use them in soft drinks. Beware. They will make you just as fat as artificial sweeteners, despite being more natural. (Neither is completely natural; both contain other ingredients.)

This unexpected effect of no-calorie sweeteners is probably the answer to another mystery. Generally people lose weight quickly on low-carb diets (if they can stick to them), but occasionally they don’t lose weight at all. I suspect that when they don’t, it’s because they’re using no-calorie sweeteners on a daily basis.

On the plus side, it appears that low-carb diets are more restrictive than they need to be. With the new research on fructose, there is speculation that low-carb diets only work because they reduce added sugar. Starch breaks down only to glucose, and so should not harm health or cause obesity – especially not starch that contains the original fiber, such as whole grain. This is Robert Lustig’s view [VIDEO], and for what it’s worth (sample of 1), it’s my experience. I gain weight from sugar, but not from starch. (Note that commercial bread contains sugar – if you want sugar-free bread, you’ll need to start baking.)

Try to Wean Yourself Off Sweetened Beverages

One of the most unfortunate habits you can get into is drinking sweetened beverages in place of water. Studies show that the body doesn’t know how to compensate for liquid calories. If you drink 600 calories of sweetened beverages, you don’t then eat less food. The body seems to assume that liquid intake is water and calorie-free. Also, as we saw in Part 1, sugared beverages are especially fattening – even more so than solid desserts – because they hit the liver so quickly.

Fruit juice is not a healthy alternative. As a beverage, it’s as bad for you as sugared soda. When you mix it with tea or seltzer, it’s no different from adding sugar. See Part 1 for why.

Unfortunately, artificially sweetened beverages are not a solution because they make you gain weight for a different reason.

There really is no way that you can get away with a sweetened beverage habit without gaining weight. So if you’d like to lose weight without dieting, weaning yourself off sweetened beverages is a surprisingly effective way to do it. It’s one of the single healthiest changes you can make to your eating habits. Sweetened beverages are just a habit – you can do this. It’s in your DNA to like water. I mainly drink water or seltzer, and I prefer unsweetened tea and coffee. I drink herbal tea plain, and put milk in black tea or coffee to break the acid. You might think you couldn’t possibly get used to this, but you can, and I really encourage you to try.

In the final article in this series, Part 4, I’ll talk about sugar addiction – why going without sugar for even a day (or giving up sweetened beverages) can feel so impossible. Are the cravings physical, emotional, or both, and how do you break free?

23 comments to Artificial Sweeteners Make You Fat

In my case, I find this is totally opposite to the truth. I drink a lot of diet sodas. I used to drink them when I hyper-morbidly-obese (330 lbs in a 5′4 frame) but of course that kinda gave me “permission” to splurge on other things like “oh since I am saving calories on this then I can eat this whole chocolate cake”. This is how my mind works. I dont think it is my body, it is just my mind…
Point being, since I stopped bingeing and I followed a “healthier” food plan I have lost 130 lbs (in abt 2.5 yrs). I never stopped drinking diet sodas and I actually drink a lot of them. When I was really heavy they were helpful with keeping my stomach full so I never thought it was a bad thing. I know they are not great for my health but being obese is not either… I am not saying everybody should drink them but it worked for me so I think it is OUTRAGEOUS to blame the diet sodas for obesity. I think people should worry about the amount of calories and quality of calories they consume and then try to cut on sodas naturally because I agree, they are not good for you in the long run. But if you want to lose weight, you dont have to become a “monk” and be all healthy and never have a “treat”. That is my experience at least…

Oh, and by the way, I did completely cut on refined sugar and simple carbs (and even fruit) for a few months and then I didnt eat refined sugar and white flour for about a year. I did all to clean my blood. Now I eat those things in small qualities. For me having “forbidden foods” doesnt work at all (with anything). The minute I feel “restricted” I get up and sleep-eat so that doesnt help either.
I like this website and I have learn a lot from it but I have also read other books and went to OA and ABA for support. I take what I need from everybody and I have found what works for me, hopefully in the very long run but one day at a time…

i love the post about artificial sweetners. i was waiting for it to give them up once i learned how they could make you fat. i’ve been on a low carb diet for a while, but have been using sweetners and zero calorie sodas and waters. now i know why i’m not losing much weight. thank you.

Congratulations on losing 130 pounds! That is wonderful. You said you are 5′4″ and started at 330 pounds, so you are now 200 pounds?

You said that to lose this weight, you stopped bingeing on whole chocolate cakes and the like, but continued to drink large amounts of diet soda. Are you still losing weight? I ask because 200 pounds is still high for 5′4″.

The studies I wrote about in my blog post don’t say that if you drink diet soda, you can never lose any weight, or that diet soda is some kind of magic potion that prevents any weight loss ever. The studies show that daily use of diet soda increases your appetite and slows your metabolism, so if you start at a normal weight, you will gain. You’re starting at a high weight, so you might see a different pattern. For example, you may be able to lose a certain amount of weight by no longer bingeing, but then get stuck and not be able to lose more while you continue to drink diet soda.

That doesn’t mean that you have to stop drinking diet soda. For you, the compromise of 200 pounds may be sufficient, and you may be happy and satisfied at that weight. Everyone is entitled to make their own choices according to their own values.

I am only giving information here, not telling anyone what to do. The information, however, is solid. Diet soda does have this effect on the body.

Great article. I had to stop using artificial sweeteners years ago, because I was having side effects from them. I tried to lose weight for several years, but just could not. I realized I had to change “what” I was eating, because I wasn’t a person who ate large amounts of food. So I cut out white foods, i.e. white sugar, white flour, white potatoes, etc. and I began to eat more whole foods, whole grains, fresh fruit (limited), etc. I have lost 22 pounds since April. I am not dieting, not counting anything, not weighing anything, just changed what I was eating. I am also exercising daily on my treadmill. It’s amazing to me how much better real food tastes, now that I am not eating processed foods. Also, I do not eat bread of any kind, except corn bread occasionally (made with no flour). If I eat bread at all, my weight loss stops and I still have about 70 pounds to lose.

Dr. Atkins noted that the simple taste of sweet (whether caloric or not) will cause an insulin release. In a pre-diabetic person that insulin release could be overblown and result in low blood sugar. The body’s response to low blood sugar is a drive to eat. That kind of eating is a drive that will occur even if the person isn’t feeling hungry. In my case, with two type 2 diabetic parents who are not overweight and my own blood sugar issues, I can only eat “normally” if I am careful about carbohydrates — all of them. As long as I avoid, I feel like and live like a normal person when it comes to my appetite and energy levels. Foods have a hormonal effect. A person struggling with an abnormal appetite needs to educate him or herself about that. Read Dr Taubes’ “Why We Get Fat and What You Can Do About It.” That said, I wonder if the extra weight gained by the group eating artificial sweeteners was due to a stronger insulin release because artificial sweeteners have a sweeter taste than natural sweeteners.

Thank you Sheryl for your response. I think it is an interesting discussiong. I do believe that for me, it is a good compromise since it is better to weight 130 lbs less now and not having to give up everything! I am aware that artificial sweetners are not good for your health and I appreciate the info, I just worry that many people will be soo scared and feel deprived they will never keep this “way of eating” for the long run. I have other friends that have lost a bunch of weight and they dont drink diet sodas and I think it is great… I am just not ready yet for that level but i want to give hope that it is possible to make some improvements and get better and then, hopefully I will get cleaner and cleaner…

Speaking about studies a friend just sent me this which I thought was interesting too:

Lea, that is great to hear! I do notice that I “crave” more whole food now, Love my veggies for example! Something I learn is that when you really allow yourself to eat anything with no shame or guilt and you really listen to your body, you naturally want good things for you! That thing about NO SHAME NO GUILT AND LISTENING TO YOUR BODY I totally owe it to you Sheryl!!! Thank you!!!
I was eating dark cherries yesterday for example and thinking, WOW this is soo much better than CANDY!

Oh, and i just want to say, even though the doctors want me to lose more weight (and i know i will) I look pretty darn good for 200 lbs!!! Honestly, weight stopped being my number one focus to become just one more thing in my life, whether it takes a year or 5 I know I will get to whatever weight I need to be in… I have a lot of FAITH on that… I just wished I could show u some pics here!!!

Thank you for this, Sheryl. I gave up diet drinks when I started my NE journey. I think I read about them in Diana Schwarzbein’s books and her point of view really resonated with me. I had not been drinking tons of them, but I definitely felt good letting them go.

I took a look at the NY Times link you posted. I disagree with the writer. While it’s true that carbohydrates cause water retention, there is much more to the story. It’s not just “calories in, calories out”. The body is very complex, and hormones play a big role. Take a look at Part 1 of this series.

I find the studies on this fascinating as years ago when I was in nursing school and queuing up diet cola machine with all the other stressed out/struggling with their weight nursing students I looked around and thought, “I wonder if this stuff makes people fat?” and “It would be interesting to do a study on this.”

Not surprised at all that art sweeteners cause obesity. Unfortunately I still struggle to eliminate the habit completely. For the most part I have recently chosen to drink regular soda if I “must” have a soft drink, so that my struggle is at least all in one category now- cutting down on real sweeteners.

Getting to the point of only putting water down the hatch is my dream…baby steps though. Tried cold turkey and restriction thing got too strong.

I did a lot more research on artificial sweeteners than made it into this blog post – stuff about the dangers (chemical aspects) and how they are in our water supply. I’ll post the rest in a second blog post.

Very interesting! I have been using Stevia daily to calm my sugar cravings. I even bought several cookbooks using stevia. Now I know why my weight loss has stopped. Not sure how to sweeten my oatmeal as I am trying to become sugar free. Would pure maple syrup be a better choice?

It’s funny you mention oatmeal. That was a puzzle for me, too. I remembered when I was growing up, a woman who cleaned our house used to eat oatmeal without any sweetener at all, which I – especially as a child – found completely unbelievable and inconceivable. I must have been 8 years old, and yet I still remember questioning her about it decades later.

I have changed my own habits significantly since writing these articles, and I now put a cut-up apple in my oatmeal with lots of cinnamon and some milk – no sweetener. Believe it or not, it’s delicious. I have found that my tastes were corrupted by eating everything with heightened sweetness, and since I’ve stopped doing that, I am able to enjoy other tastes and to appreciate more subtle sweetness. Also, the craving for intense sweetness has evaporated. I’m planning to write more about this in Part 4.

This series on sugar and artificial sweetners is outstanding and very helpful.

I am particularly interested in learning more about the “myth” that artificial sweetners do not evoke an insulin respnse in the body. My belief, based upon past learning material, is that while the chemical artificial sweetners are toxic and potentially very harmful to the body, stevia is a “natural” sweetner and therefore a much better choice than either sugar or the other more common artificials.

Are you able to provide links to any “independent scientific studies” that support the assertion that stevia confuses the body. Its not that I am taking issue with what you are saying about this. You do a great job here and your articles are all very informative. I would however, like to be able to site the specific study that supports this as I have read the same sort of comments in other articles but not seen any specific studies mentioned.

That article has a link to the research review about artificial sweeteners and insulin response (the myth is that artificial sweeteners do stimulate an insulin response; they do not), plus there are sections about stevia and other no-calorie sweeteners with more information.

I did not find any studies of the no-calorie sweetener effect done with stevia specifically (and I even wrote to the scientist heading up this research to ask – she didn’t write back). But it was done with two completely different no-calorie sweeteners plus a fat substitute, and ALL THREE showed this effect. Also, if you read the details of the studies, with the way they are designed and controlled, there is no way to explain what’s happening except by a learning effect (associating sweetness or the taste of fat with zero calories). If this is what’s happening, the exact make-up of the substance is irrelevant. The authors of the study extend their findings to all no-calorie sweeteners and stopped testing different ones after the second one gave the same results (and the fat substitute did, too). There is no reason why the findings would not apply to stevia.

Take a look at the second article for more on stevia and why the “natural” label is misleading. “Natural” does not mean “good for your health”.

Hi Cheryl, this is very interesting. I had a time in my life when i “had to” drink a diet coke every day. I craved the stuff if I didn’t have it and believe it is very addictive. Possibly because of the caffeine and phenylalanine mix which have a additive affect on each other. Anyhow that was years ago and I haven’t drunk them or other diet drinks since as I don’t like the aftertaste.

A few years after that I was “sugar free” which for me meant I still had maple syrup and honey but no processed sugars. Recently I have returned to this way of eating and have found it profoundly easier to know when I am full and when I am hungry, and, has increased my energy levels. Although I am not 100% rigid with it and when I eat food high in sugar – such as cake, I get extremely foggy in the head and extremely tired. I have always noticed that when I start the day with a breakfast with high sugar and refined carbs – that’s it I crave them all day! (So I was interested in the article you linked in about low carbs

I have been wondering if what I have is candida – as I react so strongly to sugars. Although I have trouble losing weight (even when cutting out all carbs and going to the gym) I’ve been tested for blood glucose levels (normal but I wasn’t fasting) and have normal cholesterol and low blood pressure, I am overweight by about 20kg. I’m not sure if I have metabolic syndrome but my Doctor (conventional) didn’t think so.

Meanwhile I continue to experiment with other sweeteners. I have found that if I eat something low in sugar very slowly – then I taste the sweetness! This fascinates me as I always used to eat quickly. Also I find that if I have maple syrup – I don’t get foggy in the head or cravings for more sweet things, even in the morning (that is what I like on my oatmeal lol). But that is perhaps because I have so little. I’ve read that if we keep our sugars below 15gms a day then the insulin response is not triggered.

I was also wondering what you know about xylitol? This sweetener has been seen as safe unlike other artificial sweeteners. Did you read anything about it?

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